Mass spectrometer



I Oct. 16, 1956 Filed Sept. so, 1953 w. c. WILEY 2,767,317

MASS SPECTROMETER 5 Sheets-Sheet 1' PULSE FORM/V6 C/R C U/ 7' INVENTOR.

' MAL/AM C h/lLE Y BY V MK-W ATTORNEY Oct. 16,1956 w. c. WlLEY MASS SPECTROMETER INVENTOR. MLL/AM c. MLEV Oct.'16, 1956 w. c. WILEY 2,

MASS SPECTROMETER Filed Sept. 50, 19,55 3 shets-sheet s POM/7? JUFPL V INVENTOR. -W/LL/AM c. MLEV WQ-QQE ATTOR/VE V grub MASS srEcrnoMn-mn William C. Wiley, Detroit, Mich assignor to Bendix Aviation {Iorporatiom Detroit, li/licln, a corporation of Delaware Application September 39, 1953, Serial No. 383,170

Ciaims. or. 250-413) This invention relates to mass spectrometers and more particularly to mass spectrometers for determining the masses of different ions by measuring the time required for the ions to travel through a particular distance.

In certain types of mass spectrometers, a plurality of ions are formed from the molecules of the different gases and vapors in an unknown mixture. After a considerable number of ions have been formed, an electrical force is applied to the ions to produce a movement of the ions from their place of retention. The ions of light mass have a greater velocity imparted to them than the ions of heavy mass. This causes the ions of light mass to travel through a particular distance before the ions of heavy mass. By measuring the relative times at which the ions of different mass are detected, the masses of the difierent mole-' cules and gases in the unknown mixture can be determined.

The mass spectrometers which have been disclosed thus far retain the plurality of ions in a planar configuration. All of the components which are utilized also have a planar configuration. This invention provides a mass spectrometer which utilizes the principle of time of flight to provide a delineation between the ions of different mass and which includes components of nonplanar configuration. Specifically a mass spectrometer is disclosed having cylindrical components. By utilizing such cylindrical components, advantages are obtained in the ease of fabrication of the components and in the minimization of any space charge difiicultics.

An object of this invention is to provide a mass spectrometer for determining the masses of dilferent ions by measuring the times required for the ions to travel through a particular distance.

Another object is to provide a mass spectrometer of the above character which utilizes components having nonplanar configurations to produce pulses of ions having configurations corresponding to those of the components.

A further object is to provide a mass spectrometer of the above character which utilizes cylindrical components to produce pulses of ions having cylindrical configurations.

Still another object is to provide a mass spectrometer of the above character having components which can be easily fabricated.

A still further object is to provide a mass spectrometer of the above character in which a relatively large number of ions can be utilized in each ion pulse by minimizing any space charge effects between the different ions.

Other objects and advantages will be apparent from a detailed description of the invention and from the appended drawings and claims.

In the drawings:

Figure l is a somewhat schematic diagram, partly in block form and partly in perspective, illustrating one embodiment of the invention;

Figure 2 is an enlarged sectional view of certain of the components shown in Figure l; and

Figure 3 is a somewhat schematic view, partly in block form and partly in perspective, illustrating another em bodiment of the invention.

2,767,317 Patented Get. 16, 1955 ice In the embodiment of the invention shown in Figures 1 and 2, a filament 10 made from a suitable material such as tungsten is adapted to emit electrons when heated. The filament 10 has a planar and a substantially ring-shaped configuration. An electrode 12 is disposed in substantially parallel relationship to the filament 10 at a relatively short distance such as A millimeter from the filament. The electrode 12 has an annular aperture 14 corresponding substantially in position and dimensions to the filamerit 10. The aperture 14 is covered by a screen made from a suitable conductive material to secure the inner and outer portions of the electrode 12.

An electrode 16 is substantially parallel to the electrode 12 at a relatively short distance such as l millimeter from the electrode. The electrode 16 has an aperture 18 corresponding substantially in shape and disposition to the aperture 14. The aperture 18 is covered by a suitable screen corresponding to that covering the aperture 14. An electron collector 20 is positioned at a relatively great distance such as 4 centimeters from the electrode 16 and in substantially parallel relationship to the electrode.

A cylindrical backing plate 22 is disposed between the electrode '16 and the collector 20 with its axis in substantially perpendicular relationship to these members. The axis of the backing plate 22 corresponds substantially to a line extending through the centers of the filament 10 and the electrodes 12 and 16. The diameter of the backing plate 22 is slightly less than the inner diameter of the filament 10.

The backing plate 22 has a cylindrical aperture which is covered by a screen 24 made from a suitable conductive material. One end of a conduit 25 is disposed within the backing plate 22 and the other end is connected to a receptacle 28 adapted to hold molecules of the difierent gases and vapors in an unknown mixture. Holes 29 are provided in the annular periphery of the conduit 26 at the end adjacent the aperture 24.

A cylindrical electrode 30 is disposed in substantially concentric relationship to the backing plate 22 and is provided with a diameter slightly greater than that of the outer diameter of the filament iii. For example, the electrode 30 may have a diameter approximately 0.4 centimeter greater than that of the filament 10. The electrode 30 has a cylindrical aperture corresponding substantially in shape and position to the aperture in the backing plate 22. The aperture in the electrode 30 is covered by a screen 32 made from a suitable conductive material.

A cylindrical electrode 34 is substantially concentric with the electrode 30 and has a diameter slightly greater than that of the electrode. For example, the electrode 34 may have a diameter approximately 0.4 centimeter greater than that of the electrode 36. The electrode 34 has a cylindrical aperture which corresponds substantially in shape and positioning to the aperture in the electrode 30. The aperture in the electrode 34 is also covered by a screen made from a suitable conductive material.

A cylindrical detector such as a collector 40 is disposed in substantially concentric relationship to the electrode 34. The collector 40 has a diameter which is considerably greater than that of the electrode 36 so as to receive the ions at the position of optimum focussing of the ions. For example, the collector 40 may have a diameter which is approximately 11 centimeters greater than that of the electrode 34. A time indicator such as an oscilloscope 42 is connected to the collector 40 to indicate the relative times at which the ions of different mass reach the collector.

A direct voltage of positive polarity is applied to the electrode 12 through a resistance 44 from a suitable power supply 46. Slightly positive voltages are also applied to the collectors 20 and 40 through suitable resistances 48 and 50, respectively, from the power supply 46. The collectors and 40 receive slightly positive voltages to attract back to them electrons secondarily emitted from them upon the impingement of charged particles. The filament 10, the backing plate 22 and the electrode 30 are connected to grounded resistances 52, 54, and-56, respectively and the electrodes 1.6 and 34 are directly grounded.

Negative pulses of voltage are respectively applied to the filament 10 and the electrode 12 through coupling capacitances 53 and 60 from a suitable pulse forming circuit 62. Positive pulses of voltage are applied to the backing plate 22 and the electrode 30 through suitable coupling capacitances 64 and 66 from the pulse forming circuit 62. These pulses are applied to the backing plate 22 and the electrode 30 after the voltage pulses on the filament 10 and the electrode 12 have been discontinued. A voltage pulse is applied to the oscilloscope 42 at substantially the same time as the electrode 30 to initiate the horizontalsweep of the oscilloscopebeam.

Although the pulse forming circuit-62 is shown in block form,'its construction and operation areknown to persons skilledin the art. For example, the Double Pulse Generator, Model 903, manufactured by the Berkeley Scientific Instrument Company, of Richmond, California may be used to produce a plurality of pulses separated from one another by variable periods of time. The pulse forming circuit disclosed in co-pending application Serial No. 288,014, filed May 16, 1952, by Macon H. Miller and William C. Wiley can also be conveniently adapted for use.

Because of the positive voltage on the electrode 12 relative to the voltage on the filament 10, the electrons emitted by the filament are accelerated towards the electlOd6.' The electrons are decelerated in the region between the electrodes 12 and 16 since the electrode 16 is at substantially the same potential as the filament 10. This prevents electrons from traveling into the region between the backing plate 22 and the electrode 30 with a sufficient amount of energy to ionize molecules of gas and vapor introduced into the region. 1

When voltage pulses of negative polarity are applied to the filament 10 and the electrode 12, the voltage on the electrode 12 becomes negative with respect to the potential on the electrode 16. This causes the electrons passing through the aperture 14 to be further accelerated in the region between the electrodes 12 and 16. The resultant increase in energy imparted to the electrons causes them to strike molecules of gas and vapor in the region between the backing plate 22 and the electrode 30 with a sufiicient energy to ionize the molecules. Most of the ions which are produced have a unitary positive charge.

The ions which are produced are retained in the electron stream because of their opposite charge relative to that of the stream. When a considerable number of ions have been produced for retention in the stream, the electron stream is cut off by discontinuing the voltage pulses on the filament 10 and the electrode 12. This makes the ions available for relatively easy withdrawal from their place of retention upon the imposition of voltage pulses on the backing plate 22 and the electrode 30.

The voltage pulses applied to the backing plate 22 and the electrode30 cause an electric field of relatively moderate intensity to be produced between the backing plate 22 and the electrode 30 and an electric field of considerably increased intensity to be produced between the electrodes '30 and 34. For example, voltage pulses of approximately +300-and +250 volts may be respectively 7 applied to the backing plate 22 and the electrode 30. As

a result of the imposition of the particular electrical fields, compensation is provided fordifierencesin the positioning and random motion of individual ions. The difierences in the positioning of individual ions result from the finite radial widthof the filament 10 and the slots 14 and 18. Difierences in the random motion of individual ions resultfrom thermal and other energy in the ions.

cause some of the ions to be traveling towards the backing plate 22 and other ions to be traveling towards the elec trode 30 at the instant that the electrical fields are applied.

Since an electric field of moderate magnitude is imposed on the ions until their movement past the electrode 30, the ions positioned relatively close to the backing plate 22 receive a slightly greater amount of energy than the ions of the same mass positioned relatively close to the electrode 30. This causes the ions relatively close to the backing plate 22 to have a slightly greater velocity imparted to them than the ions of the same mass which are relatively close to the electrode 30. In this way, compensation is provided for the difierences in positioning of individual ions. 7

After moving past the electrode 30, the ions enter into the region between the electrodes 30 and 34. Since all of the ions of each mass travel through the same distance in the region between the electrodes 30 and 34, they receive constant increments in energy. These constant increments in energy are considerably greater than the energy imparted to the ions in the region between the backing plate 22 and the electrode 30. The constant increments in energy are also considerably greater than the thermal and other energy in the ions.

Because of the constant and relatively great increments in energy imparted to the ions of the same mass in the region between the electrodes 22 and 30, any errors resulting from the thermal and other energy in the ions are dwarfed. For example, differences in the thermal energy of the ions may cause one ion to have a relative velocity of 10 as it passes the electrode 30 and another ion of the same mass to have a relative velocity of '13. By imposing constant increments ofenergy on the ions, the

' first and second ions may have relative velocities of 60 and 63 as they move past the electrode 34. The percent difierence between 60 and 63 is considerably less than the dilference between 10 and 13. 7

Other advantages are also obtained by imposing a rela-- tively great field. on the ions in the region between the electrodes 30 and 34. For example, this field causes the distance between the backing plate 22 and the position of optimum focussing of the ions to be considerably increased. Since the ions travel through an increased distance before the ions of each mass receive their optimum focus, an increased separation is obtained between the ions of different mass. This causes the resolution between ions of different mass to be materially enhanced. By measuring the relative times at which the ions of diflerent mass are detected, the masses of the ions can be easily determined. Indications as to the relative times at which the ions of different mass are detected are provided by the oscilloscope 42.

The mass spectrometer. disclosed above has several important advantages. It requires only a minimum number of components 'to provide a relatively sharp delineation between ions of different mass. The sharp delineation bea tween ions of 'difierent mass is produced because of the particular electric fields imposed on the ions and because of the relatively large number of ions which can be included in each pulse. A large number of ions can be included in each pulse without space charge difliculties since the annular construction of the electrodes causes the ions to be retained in an area having a relatively large periphery. Because of the annular construction of the electrodes and the collector, these components can be relatively easily fabricated. For example, they may be manufactured by techniques similar to those used in producing vacuum tubes for radio and television.

-In the embodiment shown in Figure 3, a mass spectrometer is disclosed having a cylindrical filament which is adapted to emit electrons when heated; Sur-' men 100 and the grid 102. The members 104. 106.

I08 and 110 correspond to the members 22, 30, 34 and 40 shown in Figure 1 and are similar in construction. A receptacle 112 which holds molecules of difierent gases in an unknown mixture is adapted to introduce the molecules into the region between the backing plate 104 and the electrode 106. The molecules of gas are introduced into the region between the backing plate 104 and the electrode 106 through a perforated bafile 113.

The electrode 108 and one end of the filament 100 are connected directly to ground. The other end of the filament 100, the backing plate 104, the electrode 1136 and the collector 110 are connected by difierent leads to a power supply 114 which maintains these members at different constant potentials. For example, the members 100, 104, 106 and 110 may be at potentials of +200, +300, +250 and +10 volts, respectively. The grid 102 is also connected to the power supply 114 through a resistance 116. The potential of the grid 102 is negative in respect to the filament 100. For example, if the filament is at a potential of +200 volts, the grid 102 may be at a potential of +190 volts. The grid 102 is also connected to a pulse forming circuit 118 through a coupling capacitance 120. The pulse forming circuit 118 may be similar to the pulse forming circuit 62 shown in Figure 1 and is adapted to introduce positive voltage pulses to the grid 102 to raise the potential of the grid to a positive value with respect to the filament 100 during application of the pulse.

When the filament 100 is heated by external means (not shown), electrons are emitted. The electrons cannot pass through the grid 102 because of the negative potential on the grid with respect to the filament. Upon application of a positive voltage pulse from pulse forming circuit 118, the electrons are pulsed through the grid 102 and the backing plate 104 into the region between the backing plate and the electrode 106 where they ionize the molecules of gas introduced into the region. The ions formed are accelerated towards the collector 110 which corresponds to the collector 40 shown in Figure 1 and produce signals on an oscilloscope corresponding to the oscilloscope 42 shown in Figure 1. In this way the masses of difierent ions can be determined without requiring the use of electrodes corresponding to the electrodes 12 and 16 shown in Figure 1. Furthermore, a separation of the ions on the basis of their mass is obtained by the imposition of constant voltages on the backing plate 104 and the electrode 106 and without the imposition of voltage pulses on these members.

It should be appreciated that the ion collector may be disposed within the ion-accelerating electrodes instead o'fin encompassing relationship to the electrodes as shown in Figures 1 and 2. With such an arrangement, the ions are accelerated inwardly towards the collector. It should also be appreciated that the members corresponding to the backing plate 2 and the electrodes 30 and 34 in Figure 1 may be provided with configurations different from the annular configuration disclosed above. For example, thebacking. plate andthe electrodes may be shaped as ellipses having substantially constant perpendicular distances between their surfaces. It is even conceivable that the backing plate and the electrodes may have curved configurations different from circles and ellipses in cross section.

Although this invention has been disclosed and illustrated with reference to particular applications, the prim-i ples involved are susceptible of numerous other applications which will be apparent to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.

What is claimed is:

1. A mass spectrometer, including, a first electrode having a curvilinear configuration, a second electrode disposed at a particular distance from the first electrode and having a curvilinear configuration corresponding to the configuration of the first electrode, means for providing a plurality of ions between the first and second elec'" trodes, means for applying a voltage pulse between the first and second electrodes to provide an electrical field between the electrodes to withdraw the ions from their place of provision and to produce aseparation of the ions on the basis of their mass, and a detector having curvilinear configuration corresponding to that of the first and second electrodes and disposed at a focal distance from the second electrode to detect the ions of each mass at substantially the same time.

2. A mass spectrometer, including, a first electrode having a curvilinear configuration, a second electrode'disposed at a particular distance from the first electrode and having a curvilinear configuration corresponding to that of the first electrode, a third electrode disposed ata partic lar distance from the second electrode and havinga curvilinear configuration corresponding to that of the second electrode, means for providing a plurality of ions between the first and second electrodes, means for apply ing; a voltage pulse between the first and second electrodes to impart a moderate amount of energy to the ions in the region between the electrodes and a greater amount of energy to the ions closer to the first electrode than to the ions closer .to the second electrode, means for applying a voltage pulse between the second and third electrodes to impart an increased amount of energy to the ions in the region between the electrodes and a substantially con stant increment in energy to the ions of each mass, and. an ion detector positioned at a particular distance from the third electrode to detect the ions and having a curvilinear configuration corresponding to that of the third electrode.

3. A mass spectrometer, including; a first cylindrical electrode, a second cylindrical electrode disposed in concentric relationship with the first electrode and at apar ticular distance from the first electrode, means for. pro viding a plurality of ions between the first and second electrodes, means for applying a voltage pulse between the first and second electrodes to produce a pulsed electric field between the electrodes for the withdrawal of the ions from their place of provision and a separation of the ions on the basis of their mass, and a cylindrical detector disposed in substantially concentric relationship to the second electrode to detect the ions after their travel through a particular distance from the second electrode.-

4. A mass spectrometer, including, a first cylindricalelectrode, a second cylindrical electrode disposed in con-' centric relationship to the first cylindrical electrode at a particular distance from the electrode, a third cylindrical electrode disposed in concentric relationship to thesec'on'dcylindrical electrode and at a particular distance" from the electrode, means'for providing a plurality of ions between the first and second electrodes, means for applying a pulsed electrical field of moderate intensity between the firsL and second electrodes to produce a separation of the ions on the basis or" their mass, means for applying a pulsed electrical field of increased intensity between the second and third electrodes to enhance the focussin'g of the ions, a detector disposed inconcentric relationship to the third electrode and at substantially the position of optimum focussing of the ions, and means for indicating the relative times at which the ions of different mass are detected.

5. A mass spectrometer, including, a first electrode having a looped configuration, a second electrode having a looped configuration corresponding substantially to that of the first electrode, the second electrode being separated by a particular distance from the first electrode, a third electrode having a looped configuration corresponding substantially to that of the first electrode, the third electrode being separated by a particular distance from the second electrode, means for providing a plurality of ions between the first and second electrodes, means for applying a voltage pulse between the first and second electrodes to impose an electrical field on the ions in the region between the electrodes to provide the ions closer to the first electrode with a greater amount of energy than the ions closer to the second region, means for applying a voltage pulse between the second and third electrodes to impose a stronger electrical field on the ions in the region between the'second and third electrodes than in the region between the first and second electrodes to provide the ions with substantially constant increases in energy, and a detector having a looped configuration corresponding substantially to that of the electrodes and separated by a particular distance from the third electrode to detect the ions traveling past the electrode.

6. A mass spectrometer, including, a first electrode having a configuration different from a plane, a second electrode having a configuration corresponding substantially'to that of the first electrode and separated from the first electrode by a particular distance, a third electrode having a configuration corresponding substantially to that of the second electrode and separated from the second electrode by a particular distance, means for providing a plurality of ions between the first and second electrodes, means for imposing a pulsed electrical field of moderate intensity on the ions in the region between the first and second electrodes until the movement of the ions past the region to provide the ions of each mass with diiferences in velocity dependent upon the initial positioning of the ions of that mass, means for imposing a pulsed electrical field of considerably increased intensity on the ions in the region between the second and third electrodes until the movement of the ions past the region to provide the ions with substantially constant increases in energy, and a detector having a configuration corresponding to that of the electrodes and separated from the electrodes by a particular focal distance to detect the ions 7 of each mass at substantially the same time.

7. A mass spectrometer, including, a first electrode having a looped configuration of smooth contour defined by a first axis and a second axis substantially perpendicular to .the first axis and having a particular dimensional relationship to the first axis, a second electrode having a looped configuration corresponding substantially to that of the first electrode and separated by a particular distance from the first electrode, a third electrode having a looped configuration corresponding substantially to that of the second electrode and separated by a particular distance from the second electrode, means for providing a plurality of ions between the first and second electrodes, means for imposing a pulsed electric field of moderate magnitude on the ions in the region between the first and second electrodes, means for imposing a pulsed electric field of considerably increased magnitude on the ions in the region between the second and third electrodes until the movement of the ions past the region, and an ion detector having a looped configuration corresponding substantially to that of the third electrode and separated by a particular focal distance from the electrode to detect the ions of each mass at substantially the same time.

8. A mass spectrometer, including, a 'first cylindrical electrode, a second cylindrical electrode concentric with the first electrode and separated by a particular distance from the electrode, a third cylindrical electrode concentrio with the second electrode and separated by a particular distance from, the second electrode, means for providing a plurality of ions between the first and second electrodes, an electrical circuit, for applying a voltage pulse between the first and second electrodes to produce an electrical field of moderate intensity between the first and second electrodes until the movement of the ions past the second electrode, an electrical circuit for applying a voltage pulse between the second and third electrodes to produce an electrical field of increased intensity on the ions between the second and third electrodes until the movement of the ions past the third electrode, and a detector disposed at the position of optimum focus of the ions to detect the ions of each mass at substantially the same time. 7 a a 9. A mass spectrometer, including, means for providing a plurality of ions in a looped configuration, means for applying a pulsed electrical field of moderate intensity on the ions in a first region having a looped configuration corresponding to that of the ions to produce a movement of the ions through the region and a separation of the ions on the basis of their mass, means for applying a pulsed electrical field of increased intensity on the ions in a second region having a looped configuration corresponding to that of the first region to produce substantially constant increments of energy on the ions of each mass and increments of energy greater than those imparted to the ions in the first region, and a detector disposed at substantially the position of optimum focus of the ions to detect the ions of each mass at substantially the same time.

10. A mass spectrometer, including, means for providing a first region have a substantially cylindrical con figuration and a particular radius, means for providing a second region having a particular radius and a substantially cylindrical configuration in concentric relationship to the first region, means for providing a pluralityof ions in the first region, means for imposing a pulsed force of moderate magnitude on the ions in the first region until the movement of the ions past the region to produce a movement of the ions towards the second region and to impart slightly greater velocities to the ions further from the second region than to the ions of the same mass closer to the second region, means for imposing a pulsed force of considerably increased magnitude on the ions in the second region until the movement of the ions past the region to impart substantially constant increments in energy to the ions of each mass and greater increments of energy to the ions than those imparted to them in the first region, a detector disposed past the second region at substantially the position of optimum focus of the ions, and means for indicating the relative times at which the ions of difierent mass are detected.

Smith May 16, 1950 Bennett Dec. 26, 1950 

